In recent years, vigorous progress has been made in the development of a next-generation automobile from which the curtailment of carbon dioxide and a reduction in oil dependence can be expected such as an electric vehicle (EV), a hybrid vehicle (HV), or a plug-in hybrid vehicle (PHV). A large electric current frequently flows in such automobile and hence an apparatus for breaking an electric current is needed for preventing secondary damage such as a fire, electric leakage, or an electric shock due to an accident or the like. A gas pressure-type electric circuit breaker that detonates or burns explosives and breaks an electric circuit with a pressure generated by the detonation or burning has been known as such apparatus (for example, Patent Document 1).
A gas pressure-type electric circuit breaker using an inflator to be placed in an automobile needs to satisfy the requirements of the ISO12097 test and an automobile manufacturer's original test in conformity therewith. For example, ISO12097-3 requires impact tests at −35° C., 23° C., and 85° C. In addition, when it is assumed that the breaker is used in an extreme cold land as described in JIS D204 as a JIS standard for automobile parts, a low-temperature test at −30° C. or −40° C. is required. To satisfy such requirements, a metal or a ceramic has been used in the housing of the gas pressure-type electric circuit breaker for an automobile. However, achieving a reduction in weight of the automobile and an improvement in fuel efficiency thereof involves the following problem. A member formed of the metal or the ceramic needs to be replaced with a member made of a resin (resinification). At the time of the resinification, a general engineering plastic resistant to heat at 100° C. or more can satisfy the requirement of a test under an environment at 85° C. At the same time, however, it is necessary to satisfy the requirement of a test under a low-temperature environment at from −35 to −40° C. In addition to such requirements, high levels of environmental characteristics (such as long-term resistance to heat at 100° C. or more (high-temperature aging resistance)) or a high level of flame retardancy to prepare for accidental ignition may be required.
Meanwhile, a polycarbonate-polyorganosiloxane copolymer (hereinafter sometimes referred to as “PC-POS copolymer”) as a polycarbonate-based material has been known as a resin material having a high level of low-temperature impact characteristic.
For example, Patent Document 2 discloses, as such PC-POS copolymer, a resin composition obtained by incorporating a polyorganosiloxane-acrylic composite rubber, a phosphorus-based flame retardant, and an anti-dripping agent into an aromatic polycarbonate resin. However, the polycarbonate resin composition comprising the phosphorus-based flame retardant has involved a problem in that both of its short-term heat resistance and long-term heat resistance are remarkably poor.
Patent Document 3 discloses a resin composition obtained by incorporating a polyorganosiloxane-acrylic composite rubber into an aromatic polycarbonate resin. Although the initial low-temperature impact characteristic of the aromatic polycarbonate resin composition improves, the composition has involved a problem in that its low-temperature impact characteristic after long-term high-temperature aging is remarkably poor.
Patent Document 4 discloses a resin composition obtained by incorporating a polyorganosiloxane-acrylic composite rubber into a resin composition formed of: a polyester containing a polycarbonate-polyorganosiloxane copolymer; and an aromatic polycarbonate. However, the polycarbonate resin composition comprising the polyester has involved a problem in that its low-temperature impact characteristic is much poorer than that of a composition that does not comprise any polyester. Although the Document describes that an average number of repetitions n of the organosiloxane constituent unit of the polycarbonate-polyorganosiloxane copolymer is preferably 40 to 60, the low-temperature impact characteristic of the polycarbonate-polyorganosiloxane copolymer is insufficient and the Document has no discussion about its low-temperature impact characteristic after long-term high-temperature aging.
Patent Document 5 discloses a resin composition obtained by incorporating a polyorganosiloxane-acrylic composite rubber into a resin composition formed of a polycarbonate containing a polycarbonate-polyorganosiloxane copolymer. Although the Document has no description about a preferred average number of repetitions of an organosiloxane constituent unit, a composition having an average number of repetitions n of 30 is described in Examples. However, the Document has no discussion about the low-temperature impact characteristic of the polycarbonate-polyorganosiloxane copolymer after long-term high-temperature aging, and the low-temperature impact characteristic remain further improvement.
As described above, the low-temperature impact characteristic of a related-art polycarbonate resin composition containing a PC-POS copolymer after long-term high-temperature aging reduces, and hence it has been unable to obtain a resin composition excellent in low-temperature impact strength after high-temperature aging.